Silver cathodes utilized in electrochemical synthesis, such as those disclosed in U.S. Pat. Nos. 4,242,183, 4,217,185, 4,460,441, and the references therein, are known to require activation to perform at high efficiency. They are further known to decrease in efficiency with use and to require periodic reactivation for continuing operations.
Activation and reactivation of silver cathodes is generally achieved by an anodization process in which the unactivated electrode is dipped or immersed in a catholyte containing water and hydroxide ions and anodically polarized, thereby converting some of the silver in the cathode surface to colloidal silver oxide, roughening and corroding the surface at the same time. The polarity of the electrode is then reversed and the oxide is electrolytically converted to microcrystalline silver which is active in electrochemical synthesis. The polarity reversal is generally repeated several times at intervals. Another convenient method of activating or reactivating silver cathodes is to add a small amount of water soluble silver salt, such as silver nitrite, to a catholyte containing water and hydroxide ions, under sufficient agitation to keep the resultant colloidal, hydrous silver oxide particles well dispersed. The silver oxide particles thus formed are reduced to electrolytically effective microcrystalline silver when a current is applied. These methods are discussed in U.S. Pat. No. 4,242,183.
The current activation and reactivation procedures are useful, but do not activate or reactivate the cathodes to their maximum possible efficiency. Since the economics of electrochemical processes are in large measure determined by the efficiency of the electrolytic cell employed, improved and simplified methods of activation and reactivation are desirable.